1. Field of the Invention
The present invention relates to a manufacturing apparatus of bonded optical disks and bonding method, for producing multi-layer optical disks consisting of two or more disk substrates.
2. Related Art of the Invention
In recent years, along with increase in the amount of information required by information equipment audio-visual equipment or the like optical disks have attracted attention as a recording medium because of their excellent capabilities to provide easy data access, store large volumes of data, and reduce the size of equipment and they have been packed with information increasingly densely. For example, the packing densities of digital video disks are made higher in the following manner: two disk-shaped molded resin substrates with signals recorded on one side are bonded with ultraviolet-curing resin or the like so that both signal layers can be reproduced from one side.
However, it is difficult to play back the disks unless the thickness of the bonding layer which bonds the two signal substrates is controlled to within a designated rage. This makes it important to improve manufacturing techniques.
Now the structure of conventional optical disks will be described below. Conventional optical disks have:
(a) a first signal substrate with signal pits formed on one side by injection compression molding or the like and a translucent film layer formed on the signal side by sputtering or the like;
(b) a substrate bonding layer formed by an adhesive such as an ultraviolet-curing resin to bond the two signal substrates; and
(c) a second signal substrate with signal pits formed on one side by injection compression molding or the like and a reflective film layer formed on the signal side by sputtering or the like.
To make an optical disk with such a configuration by a bonding method, the second signal substrate, for example, is clamped on the turning table with a vacuum chuck or the like, facing up the reflective film, and liquid-state, ultraviolet-curing resin is applied virtually concentrically by a dispenser revolving at a designated radius of the substrate.
Alternatively, the dispenser is fixed at a designated radius of the substrate and the turning table is rotated at a low speed to apply the ultraviolet-curing resin to the substrate virtually concentrically.
The second signal substrate coated with the ultraviolet-curing resin is stacked on the first signal substrate brought by substrate transport means, on the same turning table, with the surface coated with ultraviolet-curing resin and the translucent film layer facing each other. The stacked disk on the table rotates for removal of excessive ultraviolet-curing resin, deaeration, and equalization of adhesive thickness as the turning table rotates according to a spin program which specifies the number of rotations and time of rotation.
This process is intended to reduce the variations in, and improve the reproducibility of, the thickness of the ultraviolet-curing resin layer (bonding layer) in the bonded disks.
After the adjustment of the thickness, the substrates are transferred to another table and the ultraviolet-curing resin cures under the ultraviolet light irradiated from outside the table by an ultraviolet lamp or the like. The disks are transferred to another table and the thickness of the cured ultraviolet-curing resin (bonding layer) is measured by a bonding-layer thickness gauge employing a red laser beam. The measured thickness data is used to sort the disks into good disks whose bonding-layer thickness falls under a designated range and defective disks whose bonding-layer thickness falls outside the designated range. Then the two groups of disks are separated by transport means.
However, with the prior art described above, the yield in the production process of disks is lowered by variations in the viscosity of the ultraviolet-curing resin, variations in the temperature and humidity during the application of the ultraviolet-curing resin, instability of the bonding-layer thickness caused by changes in the shape of the first and second signal substrates in the case of optical-disk bonding methods using a specific spin program, and inability to readjust the bonding-layer thickness after measurement, which is made after the ultraviolet-curing resin has cured.
The present invention, which has been made in view of the foregoing problems in the prior art, provides an optical-disk bonding apparatus and method that can control the thickness of bonding layers with a high degree of accuracy.
One aspect of the present invention is an optical-disk bonding apparatus for bonding two or more disk substrates with an adhesive, comprising:
a turning table for clamping said disk substrates; a thickness gauge for measuring a thickness of bonding layers; and a rotation control unit for controlling said turning of a turning table; wherein the thickness of the bonding layers is measured with said thickness gauge on said turning table; and a rotation of said turning table or the pressure acting on said disk substrates is controlled based on the measured thickness data.
Another aspect of the present invention is the optical-disk bonding apparatus, wherein the rotation control of said turning table consists in controlling a time of rotation or number of rotations of said turning table.
Still another aspect of the present invention is the optical-disk bonding apparatus, wherein the control of the pressure acting on said disk substrates consists in controlling an intensity of pressure or duration of pressure application.
Yet another aspect of the present invention is an optical-disk bonding apparatus for bonding two or more disk substrates with an adhesive, comprising:
a first table for clamping said disk substrates; a thickness gauge for measuring a thickness of bonding layers at least at one point on said disk substrates; a second table for holding another substrate to be bonded face to face to said disk substrates; and a pressurizing mechanism for bonding said disk substrates under pressure by moving said second table and said first table closer to each other; wherein
the thickness of said bonding layers is measured with said thickness gauge; and the pressure applied by said pressurizing mechanism is controlled, based on the measured thickness data.
Still yet another aspect of the present invention is the optical-disk bonding apparatus, wherein said thickness gauge measures thicknesses at multiple points at least two radii on the disk substrates to be bonded.
A further aspect of the present invention is the optical-disk bonding apparatus, wherein said thickness gauge has at least two points of thickness measurement at the same radius on the disk substrates to be bonded.
A still further aspect of the present invention is the optical-disk bonding apparatus, wherein said thickness gauge is used as an instrument which directs a laser beam with a wavelength between 600 nm and 700 nm virtually perpendicularly onto the bonding layer of said disk substrates.
A yet further aspect of the present invention is the optical-disk bonding apparatus, wherein said turning table is made of material virtually transparent to light with wavelengths between 600 nm and 700 nm.
A still yet further aspect of the present invention is the optical-disk bonding apparatus, wherein the first table for clamping said disk substrates is a table made of material virtually transparent to light with wavelengths between 600 nm and 700 nm.
An additional aspect of the present invention is the optical-disk bonding apparatus wherein the second table for pressing another substrate to be bonded face to face to said disk substrates is a table made of material virtually transparent to light with wavelengths between 600 nm and 700 nm.
A still additional aspect of the present invention is the optical-disk bonding apparatus, wherein the first table for clamping said disk substrates comprises said pressurizing mechanism.
A yet additional aspect of the present invention is an optical-disk bonding method, wherein disk substrates are bonded while they are rotated on a turning table, a thickness of the bonding layers that bond the disk substrates is measured, and the thickness of the bonding layers is controlled to within a designated range by controlling the rotation of said turning table based on the measured thickness data.
A still yet additional aspect of the present invention is an optical-disk bonding method, wherein two disk substrates are bonded by holding them between two tables, a thickness of the bonding layer that bonds the disk substrates is measured, and the thickness of the bonding layer is controlled to within a designated range by controlling the pressing force of said tables based on the measured thickness data.